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22.1 Characteristics of the Atmosphere Characteristics of the Atmosphere Section 22.1 Atmosphere · layer of gases that surrounds the Earth · air = mixture of chemical elements and compounds in the atmosphere · functions (2) protect Earth's surface from the sun's radiation help regulate Earth's surface temperature · gases Composition of Atmosphere nitrogen - 78%, oxygen - 21%, argon, CO2, and other - 1% · water vapor enters by evaporation from oceans, fresh water, and plants most near surface decreases with height · ozone - O3 form of oxygen gas absorbs harmful ultraviolet radiation from the sun less ozone = more UV rays reach Earth's surface = sunburn and cancer thinning results from chlorofluorocarbons (CFCs) which breaks down ozone · particulates Atmospheric Pressure · pressure exerted on Earth's surface by the atmosphere · decreases as altitude increases gravity not as strong at high altitude, so air molecules move further apart and exert less pressure · decreases as temperature increases molecules move further apart as air heats up · decreases as water vapor increases water vapor is less dense (or lighter) than oxygen and nitrogen molecules dust, ash, pollen, bacteria, salt helps form fog & rain (water clings to particulates) tiny particles can stay in the air for months or years Measuring Atmospheric Pressure · tool = barometer · units = atmosphere (atm), millimeters of mercury (mm Hg), and millibars (mb) · standard atmospheric pressure at sea level = 1 atm = 760 mm Hg = 1000 mb Layers of Atmosphere · 4 layers based on temperature · troposphere = 0 - 12 km · stratosphere = 12 - 50 km contains ozone layer · mesosphere = 50 - 80 km · thermosphere ionosphere = 80 - 400 km exosphere = 400 - ? km 22.1 Characteristics of the Atmosphere · · · · Troposphere closest to Earth's surface weather occurs here contains gases essential to life temperature decreases with altitude heated by thermal energy that comes from Earth's surface · average altitude = 12 km depends on latitude and season Thermosphere · temperature increases with altitude nitrogen and oxygen absorb solar energy as high as 1000 C · ionosphere = lower portion ions formed when UV rays from sun knock electrons off oxygen atoms · exosphere = upper limit of indefinite altitude Stratosphere & Mesosphere STRATOSPHERE · strong winds and few weather changes · contains ozone · temperature increases with altitude heated by absorption of solar energy by ozone MESOSPHERE · temperature decreases with altitude · coldest temperatures in atmosphere